The present invention relates to centerflow rolled products such as webs of paper or non-woven material, and particularly to a centerflow rolled web wherein individual sheets or wipes are defined by an improved perforation line.
Centerflow rolled products are known in the art. Such products are typically coreless and dispensed by an end sheet or wipe being pulled from the center of the rolled product through a dispenser. The rolled web of material is conventionally defined into individual sheets or wipes by transverse perforation lines that define a tear line for each sheet or wipe. The perforation lines comprise alternating bonds and perforations which, in most conventional products, are of uniform length and spacing. The perforations are typically rectangular slits having a transverse orientation.
Perforating devices for defining perforation lines in any manner of rolled paper or non-woven products are also well known in the art. For example, conventional perforating devices are incorporated into almost all bathroom tissue and towel liners in a typical manufacturing and converting plant. These devices comprise a perforator roll, which holds a number of perforation (perf) blades, and a stationary anvil head which holds a number of anvil assemblies. The anvil assemblies are typically positioned helically on the stationary anvil head so as to keep all of the perf blades from striking all of the anvils at the same time. In the process, a balance must be struck between having the perforation lines with sufficient bond strength to operate efficiently without breaks on the converting equipment, and yet have a low enough bond strength to provide easy and undamaged sheet detaching for the consumer. Poor detaching has always been a major consumer issue for rolled products, and particularly for centerflow products.
Centerflow products are typically dispensed through a dispenser that incorporates a narrow opening or passage through which the end of the centerflow web is pulled. Thus, the material is bunched or gathered as it is pulled through the dispenser, and the individual wipes or sheets are pulled apart with the material in this bunched condition. Thus, the dynamics of the separating or tearing process along the perforation line defined on a centerflow product is fundamentally different from that of conventional bath tissue or paper towels wherein the product is unwound from the circumference of the roll and is typically in a flat or straight state upon being separated by the consumer. One conventional centerflow product dispenser is known in the art as the WetTask(copyright) system by Kimberly-Clark of Neenah, Wis. The WetTask(copyright) dispensing system is also described in U.S. Pat. No. 5,560,514, the entire disclosure of which is incorporated herein by reference for all purposes.
Advances have been made in the art of perforated roll products to improve the perforation line profiles. For example, U.S. Pat. No. 5,562,964 to Kimberly-Clark Corporation discloses that sheet detaching can be significantly improved by customizing the perf blades so that the perforation lines in the sheet have a lower bond length, and thus lower bond strength, at or near the outer edges of the sheet as compared to the rest of the sheet. This is accomplished according to the ""964 patent by using perf blades that provide different levels of bonding strength in the appropriate areas of the perfed sheet. The ""964 patent describes that the number of poor detachments between individual sheets decreases as the bonded lengths at the outer edges of the towel sheets are shortened. The teaching, however, according to the ""964 patent is not particularly relevant to centerflow products.
A need thus exists in the art for a perforation line profile particularly suited for the dynamics of dispensing centerflow rolled products so as to decrease the number of separation defects.
Objects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention.
According to the present invention, an improved rolled web of centerflow material, such as a paper or non-woven material, is provided wherein the material is dispensed by an end sheet or wipe being pulled from a center of the rolled web. The web is divided into individual wipes or sheets by transversely extending perforation lines. Each perforation line further comprises a varying perforation profile defined by opposite edge portions and a middle section between the edge portions. In one desired embodiment, the edge portions comprise a stronger overall bond strength as compared to at least one portion of the middle section.
The edge portions have a xe2x80x9cstronger bond strengthxe2x80x9d as compared to the middle portion in that the length of the perfs along the perforation line in the edge portions is substantially less than the length of the perfs in the weaker middle portion. The bonds may have the same length in both the edge and middle portions. For example, the perforations in the edge portions may have a length generally between about 30% to about 70% of the perforations in the middle portion, and in one desired embodiment about 45% to about 50%. In one particularly desired embodiment, the bonds have a length of about 0.032 inches along the entire perforation line, the perfs in the middle portion have a length of about 0.433 inches, and the perfs in the edge portions have a length of about 0.208 inches.
In one variation of the stronger edge embodiment of the invention, the middle section may comprise at least two weaker bonded middle portions separated by a stronger bonded middle portion such that the weaker bonded middle portions are disposed directly adjacent to the edge portions. The stronger bonded middle portion may comprise the same bond/perf profile as the edge portions. In this embodiment, the edge portions and the stronger bonded middle portion may have a length generally about twice as long as that of the weaker bonded middle portions.
As described in greater detail below, applicants have found that the perforation line profile as described above wherein the edge portions have a stronger bond strength than at least one weaker middle portion is particularly efficient in reducing overall perforation defects with centerflow rolled products.
In an alternative embodiment of the invention, the perforation line is defined by opposite edge portions and a middle portion having generally the same bond strengths. An intermediate portion is disposed between each of the edge portions and middle portion, with the intermediate portion having a different bond strength than the edge and middle portions. The edge and middle portions may have a length generally about twice as long as that of the intermediate portions.
In an example of this embodiment particularly useful for reducing total perforation defects, the edge portions and the middle portion have a stronger bond strength as compared to the intermediate portions.
In an example of this embodiment particularly useful in reducing roping/streaming defects, the edge portions and middle portion have a weaker bond strength as compared to the intermediate portions.
The length of the edge portions, middle portion, and intermediate portions will depend on the profile of the individual perforation blades, as well as the blade pattern across the entire perforation line. For example, as explained in greater detail below, a perforation blade particularly useful with the present invention has a length of 4.5 inches and is divided into three distinct perforation sections. The blade may have a weak/strong/weak profile wherein the length of the perfs in the strong section is less than the length of the perfs in the edge sections. Alternatively, the blade may have a strong/weak/strong profile wherein the length of the perfs in the weak middle section is significantly longer than the length of the perfs in the stronger edge sections.
The perforation blades are aligned end to end and, for example, four such blades would define an 18 inch perforation line. A typical 12 inch web of material would then be positioned along the perforation line to obtain the desired perforation profile across the web. For example, if four strong/weak/strong profile blades are aligned end to end, and the web of material positioned relative to the blades so as to define stronger edge portions along the perforation line, the stronger edge portions are defined by adjacent strong sections of adjoining perforation blades. The edge portions thus have an overall length twice as great as the intermediate weak middle portions that are directly adjacent to the edge portions. Thus, the perforation lines defined with the perforation blades described herein will have an alternating perforation profile. The profile may comprise strong edge portions and a strong middle portion with weaker intermediate middle portions defined between the strong edge portions and strong middle portion. Alternatively, the profile may comprise weak edge portions and a weak middle portion with strong intermediate middle portions defined between the weak edge and middle portions. Each profile has certain beneficial aspects, as described in greater detail below.